This invention relates generally to an image-reading apparatus having a deviation correcting function and, more particularly, to an image recorder apparatus of the type noted above, in which an original image is read out by charge-coupled devices capable of photoelectric conversion.
Recently, with rapid development of office automation, there has been a demand for an image reader for use in copying machines, facsimile sets, etc., which can perform high-speed and high-resolution reading of image data and is small in size. To meet this demand, image readers using close-contact type image sensors have been developed and used in practice.
In the image reader noted above, a focusing-light lens is used for an optical system connecting optical face and image sensor, and an image sensor is disposed in the vicinity of the original surface for reading image data. In other words, the width of reading of the original is the same as that of the original so that the original image is focused on the same scale on the image sensor. The image sensor of the close-contact type, which provides the same reading width as the original width, comprises a plurality of charge-coupled device image sensor elements (hereinafter referred to as CCD elements) in a staggered arrangement (parallel and alternate arrangements).
When reading image data using the image sensor of the above construction, it is necessary to correct positional (i.e., spatial and time-wise) deviation of the CCD elements according to the speed (or reading density) at which an original is scanned in a secondary scanning direction perpendicular to the scanning direction of the image sensor. Each CCD element has a line memory (or line shift gate), so that the correction is done line by line.
Denoting the positional deviation between first and second rows of CCD elements among the CCD elements in the staggered arrangement noted above by g .mu.m, and the scanning speed in the secondary scanning direction by Vx .mu.m/sec., a positional deviation is produced in the read-out image in correspondence to the displacement of the CCD elements in the two rows in an optical signal time t according to the scanning speed Vx .mu.m/sec. Accordingly, the time at which the first row CCD elements provide output, is delayed for a predetermined number of lines while setting the same timing of fetching optical signal, i.e., storage timing, for the first-and second-row CCD elements. In this way, the positional deviation between the first and second row CCD elements is corrected. For example, where the line width of the reading density in the secondary scanning direction is one half of g, the output of the first-row CCD elements is delayed for two lines. That is, the output of the first-row CCD elements, which read out image data first, is delayed for a number of lines, corresponding in number to the positional deviation of the line shift gate. Therefore, the output of the second-row CCD elements, which read out image data subsequently, is simultaneously obtained. In this way, a read-out image free from distortion is obtained.
Where the correction is done line by line in the manner as described above, however, a deviation for at most 0.5 line (Vxta) results in the read-out image with respect to the displacement Vxt of CCD elements in the optical signal storage time t when the reading density, i.e., reading line density, is varied continuously, not stepwise, by varying the speed of scanning of the original. In other words, perfect correction can not be obtained when the displacement Vxt of CCD elements noted above is not an integral multiple fraction of the positional deviation of the CCD elements, that is, when the deviation of the CCD elements is not an integral multiple of the line width of the reading density.